LEDs have indeed evolved by leaps and bounds: a few years ago, it was virtually impossible to get LEDs powerful enough to be used as headlights, but nowadays LED headlights are everywhere. The highly efficient LEDs have a very long lifetime and allow great freedom for the designer.
Image borrowed from www.audi.se
Click on the image to access the Audi film on LED headlights.
But the high thermal radiation of diodes is still a concern for designers. There are several reasons for this:
- LEDs generate at best about 34 % light of input energy, while 65 % radiates as heat.
- The heat reduces both light output and lifetime.
- The high temperature also shifts the dominant the wavelength of light, which leads to colour shifts.
A great way to keep heat at bay is to use silicone to conduct heat away, e.g. to a heat sink.
Silicone-based materials for heat dissipation have a wide range of technical advantages, including
- They can withstand high heat really well, even for a long time. 200°C is no problem.
- They have very low surface tension, providing the best possible surface contact with the LED chip and with the heat sink. This maximises the transferred thermal energy.
- It is easy to automate a production line with a silicone adhesive or grease. Fast production can be easily fixed.
The picture below shows the dramatic effect that the right thermal conduction can have on the temperature of an LED. The more yellow and red the image shows, the higher the temperature is at that point. The image on the right shows an LED device with a much lower temperature and more symmetrical heat distribution.
Tribotec currently offers more than 20 different silicone materials for heat conduction. We have several products designed for gluing and/or moulding. With an adhesive, no further attachment of the heat sink is needed, but there is also grease if you want to be able to dismantle the parts easily. A grease will always remain soft and uncured. At the same time, a grease can be made highly thermally conductive. The latest products are also optimised to minimise the so-called bleeding of oil even at high temperatures and for long periods.
Please read the technical data in Momentive's brochure which shows a selection for heat conduction (in English called Thermal Interface Management, TIM), and get in touch with us and we'll help you find the right product for the right application.
